The present invention relates to an apparatus for determining the mechanical deformation behavior of extrudable measuring samples, wherein two drivable take-up rollers are disposed pairwise on a resiliently deflectable mounting arrangement, and to which an extruded measuring sample billet is supplied.
Such apparatus, which are commonly called extension testers, are utilized in synthetic material processing where the maximum extensibility and the tensile strength of the synthetic material melts are determined in order to determine the highest possible processing speed. For this purpose an extruded measuring sample billet is supplied to a take-up apparatus having a pair of take-up rollers, and the sample billet is continuously elongated at continuously increasing take-up speed. The bearing force exerted in the process onto the pair of take-up rollers is measured and drawn on for evaluating the tensile strength at tearing of the measuring sample billet.
DE 19 04 079 describes an apparatus for determining the mechanical deformation behavior of extruded measuring samples, which comprises a pair of take-up rollers drivable at a variable rotational speed and which are resiliently supported in the direction of transport of the measuring sample. The take-up rollers are for that purpose mounted on a resiliently supported carrier. To determine the mechanical deformation behavior of a measuring sample, the deflecting force acting at given rotational speed of the take-up rollers on to the take-up rollers, respectively the support, is measured continuously.
The take-up rollers often have a corrugated or indented surface in order to prevent the measuring sample billet from slipping through while it is being pulled out. As a rule, the measuring sample billet has a cross section between 2 mm and 3 mm and, during the pulling-out between the take-up rollers, is rolled out to approximately 1 mm.
The use of the known extension tester is frequently problematic in practice since in the case of a large portion of the conventionally used polymers, such as for example polypropylene (PP), polycarbonate (PC) and polyamide (PA), the polymer billet adheres to the take-up rollers which can be traced back to the pronounced "sticking effect" of these polymers in the melt state. This sticking effect not only occurs when the polymer billet is guided between the take-up rollers but rather also when the polymer billet is guided in front of the rotating take-up rollers, thus, across the front faces of the take-up rollers, wherein the extruded measuring sample billet is elongated across the touching contact at the rotating front faces.
It is an object of the present invention to provide an apparatus for determining the mechanical deformation behavior of extrudable measuring samples of the type under consideration, and to develop it further such that the adhesion of the measuring sample billet on the take-up rollers is as much as possible avoided and, in particular, is avoided for measuring samples with low viscosities.